Domínios dos escoamentos em eventos ENOS: Estação Fluviométrica Ponte da Batalha/PB.

Abstract

The hydrograph refers to the time series of flows that records the water potential in a river section, summarizing the balance of water inflow and outflow in a watershed. In perennial rivers, seasonal variation is observed in the months when the stream is gaining or losing in relation to the aquifer throughout the hydrological year. Thus, flow separation techniques are employed to estimate the quantity of underground (or base) flow and/or surface runoff in a given period, also allowing the quantification of the dominance of these contributions through flow indexes (BFI – Base Flow Index). In this study, three methods of base flow separation in hydrographs were applied using digital filters: Fixed Interval (FI), Moving Interval (MI), and Local Minimum (LM). The flow time series used came from the Ponte da Batalha fluviometric station, located in the municipality of Cruz do Espírito Santo, in the Lower Course Region of the Paraíba River, in the state of Paraíba, Brazil. The choice of this station and study area was due to the availability of a continuous and gap-free data series from Jan/1970 to Dec/1985, selected from the broader database (Dec/1969 to Dec/2024) provided by the National Water and Sanitation Agency (ANA), through the HidroWeb Portal. In this selected time series, base flow indexes were calculated during the climatological ENSO events: El Niño and La Niña, including neutral periods. In all analyzed methods (FI, MI, and LM), the greatest base flow dominance occurred during the months of total flow recession, especially from September to December and from January to February. The Local Minimum (LM) method yielded the highest values for the proportion of groundwater flow. The discretization of El Niño and La Niña months offered a specific view of the climatological influence on the applied flow separation methodologies: during La Niña periods, the average base flow indexes were lower, yet very close to the values observed during El Niño periods; in neutral periods, the condition of higher base flow dominance was recorded. The results obtained aim to support water resource management instruments in the study area, such as water use permitting and raw water charging, especially in the quantitative context of flow partitioning, applied in perennial rivers, discretized according to the highlighted climatologies.